Oxygen isotope ratios in olivine from the Hawaii Scientific Drilling Project

Oxygen isotope ratios of olivine in 23 tholeiites from the Hawaii Scientific Drilling Project (HSDP) core (15 from Mauna Kea, 8 from Mauna Loa) and three samples of outcropping subaerial or dredged submarine Mauna Kea lavas have been measured by laser fluorination. The δ^(18)O values are 4.6–5.4 ‰, confirming previous observations that some Hawaiian lavas are derived from sources with δ^(18)O values lower than typical upper mantle (δ^(18)Oolivine ≈ 5.2±0.2 ‰). The Mauna Kea-Mauna Loa transition marks a shift from δ^(18)O values lower than the mantle average in Mauna Kea olivines (∼4.8) to more typical mantle values in Mauna Loa olivines. Lavas containing olivines with δ^(18)O values similar to the typical upper mantle are associated with more “primitive” or less depleted radiogenic isotope characteristics; i.e., with higher ^3He/^4He (>13 Ra), higher ^(87)Sr/^(86)Sr (>0.7036) and lower є_(Nd) (<6.5), and with ^(206)Pb/^(204)Pb ratios less than -18.3. These relationships indicate that the δ^(18)O values of the relatively enriched source components of the Hawaiian plume sampled by Mauna Loa lavas are comparable to (or greater than) the mantle average. This conclusion is supported by δ^(18)O values of olivine from other high ^3He/^4He islands, which are also comparable to the upper mantle average. The low δ^(18)O values in Hawaiian lavas are derived from a source having more MORB-like, or depleted, He, Nd, and Sr isotope ratios, but more radiogenic Pb than is seen in the Mauna Loa lavas Assimilation of ^(18)O-depleted lower oceanic crust from the underlying Pacific crust by hot, MgO-rich parental magmas or melting of older, recycled oceanic crust entrained in the Hawaiian plume are both possible sources of this ^(18)O-depleted, MORB-like component in Hawaiian magmas

Letters between Eiler Freece and W. J. Kerr

Letters concerning a position in Utah Agricultural College

Stable isotopic characteristics and magmatic history of meta-igneous rocks, Adirondacks, NY

The Adirondack Highlands contain dominantly meta-igneous rocks including the anorthosite-granite association and a wide variety of unrelated orthogneisses from gabbroic to granitic composition. The internal variation of oxygen isotopes within Adirondack meta-igneous suites related to the Marcy anorthosite shows that elevated δ^(18)O is a compositionally dependent characteristic of the protolith. Analysis of δ^(18)O in previously unsampled compositions in this suite has led to a stable isotopic, petrographic and major element description of a continuous range of rock types from two-pyroxene, oxide rich monzonitic gneiss to mesoperthite, quartz rich granite gneiss within the Tupper and Saranac sheets on the NW margin of the Marcy anorthosite. This expanded data set has allowed the formulation of a semi-quantitative model, based both in thermodynamics and mass balance, for the AFC magmatic evolution of this suite. A sampling traverse of the Snowy Mountain dome anorthosite and related halo of granitic gneiss in the southern Adirondack Highlands shows the concentric spatial distribution of δ^(18)O in granites around anorthosite, constrains the extent of interaction between anorthosite and granite, and provides an additional example of crustal interaction in the magmatic evolution of this suite. This evidence, combined with previous work (Morrison and Valley, 1988), documents extensive crustal interaction in region-wide anorthosite-granite plutonism prior to the peak of Grenville metamorphism

Oxygen-isotope and trace element constraints on the origins of silica-rich melts in the subarc mantle

Peridotitic xenoliths in basaltic andesites from Batan island in the Luzon arc contain silica-rich (broadly dacitic) hydrous melt inclusions that were likely trapped when these rocks were within the upper mantle wedge underlying the arc. These melt inclusions have been previously interpreted to be slab-derived melts. We tested this hypothesis by analyzing the oxygen isotope compositions of these inclusions with an ion microprobe. The melt inclusions from Batan xenoliths have δ 18OVSMOW values of 6.45 ± 0.51‰. These values are consistent with the melts having been in oxygen isotope exchange equilibrium with average mantle peridotite at temperatures of ≥875°C. We suggest the δ 18O values of Batan inclusions, as well as their major and trace element compositions, can be explained if they are low-degree melts (or differentiation products of such melts) of peridotites in the mantle wedge that had previously undergone extensive melt extraction followed by metasomatism by small amounts (several percent or less) of slab-derived components. A model based on the trace element contents of Batan inclusions suggests that this metasomatic agent was an aqueous fluid extracted from subducted basalts and had many characteristics similar to slab-derived components of the sources of arc-related basalts at Batan and elsewhere. Batan inclusions bear similarities to “adakites,” a class of arc-related lava widely considered to be slab-derived melts. Our results suggest the alternative interpretation that at least some adakite-like liquids might be generated from low-degree melting of metasomatized peridotites

The Effects of Metamorphism on Iron Mineralogy and the Iron Speciation Redox Proxy

As the most abundant transition metal in the Earth’s crust, iron is a key player in the planetary redox budget. Observations of iron minerals in the sedimentary record have been used to describe atmospheric and aqueous redox environments over the evolution of our planet; the most common method applied is iron speciation, a geochemical sequential extraction method in which proportions of different iron minerals are compared to calibrations from modern sediments to determine water-column redox state. Less is known about how this proxy records information through post-depositional processes, including diagenesis and metamorphism. To get insight into this, we examined how the iron mineral groups/pools (silicates, oxides, sulfides, etc.) and paleoredox proxy interpretations can be affected by known metamorphic processes. Well-known metamorphic reactions occurring in sub-chlorite to kyanite rocks are able to move iron between different iron pools along a range of proxy vectors, potentially affecting paleoredox results. To quantify the effect strength of these reactions, we examined mineralogical and geochemical data from two classic localities where Silurian-Devonian shales, sandstones, and carbonates deposited in a marine sedimentary basin with oxygenated seawater (based on global and local biological constraints) have been regionally metamorphosed from lower-greenschist facies to granulite facies: Waits River and Gile Mountain Formations, Vermont, USA and the Waterville and Sangerville-Vassalboro Formations, Maine, USA. Plotting iron speciation ratios determined for samples from these localities revealed apparent paleoredox conditions of the depositional water column spanning the entire range from oxic to ferruginous (anoxic) to euxinic (anoxic and sulfidic). Pyrrhotite formation in samples highlighted problems within the proxy as iron pool assignment required assumptions about metamorphic reactions and pyrrhotite’s identification depended on the extraction techniques utilized. The presence of diagenetic iron carbonates in many samples severely affected the proxy even at low grade, engendering an interpretation of ferruginous conditions in all lithologies, but particularly in carbonate-bearing rocks. Increasing metamorphic grades transformed iron in carbonates into iron in silicate minerals, which when combined with a slight increase in the amount of pyrrhotite, drove the proxy toward more oxic and more euxinic conditions. Broad-classes of metamorphic reactions (e.g. decarbonation, silicate formation) occurred at distinct temperatures-pressures in carbonates versus siliciclastics, and could be either abrupt between metamorphic facies or more gradual in nature. Notably, these analyses highlighted the importance of trace iron in phases like calcite, which otherwise might not be included in iron-focused research i.e. ore-system petrogenesis, metamorphic evolution, or normative calculations of mineral abundance. The observations show that iron is mobile and reactive during diagenesis and metamorphism, and these post-depositional processes can readily overprint primary redox information held by iron speciation. However, in principle, additional mineralogical and petrographic approaches can be combined with iron speciation data to help untangle many of these post-depositional processes and arrive at more accurate estimates of paleoenvironmental redox conditions and processes, even for metamorphosed samples

Stable isotopic disequilibrium in high-T metamorphic systems

A principal use of stable isotopes in metamorphic rocks is as thermometers, or as tests for isotopic equilibrium where metamorphic temperatures are known. Applications are often complicated when apparent isotopic temperatures are discordant and disagree with petrologic temperatures, indicating a failure of isotopic systems to record and/or preserve equilibrium, peak-T fractionations. In low-T, fluid-hosted environments such features often clearly reflect open system exchange. However, in high-T metamorphic environments a slow cooling history can be sufficient to produce such features by retrograde, closed system exchange between coexisting minerals

Isolation and characterization of Bacillus thuringiensis from soils in contrasting agroecological zones of Ethiopia

Phenotypic and molecular methods were used to isolate and characterize B. thuringiensis from diverse agro-ecological zones of Ethiopia. Bioassays were used to test the insecticidal activity of B. thuringiensis strains against the major malaria vector, Anopheles arabiensis (Diptera).  B. thuringiensis were isolated from 32% of the total 503 soil samples collected from the 16 agro-ecological zones. All sequenced isolates were 99%–100% identical to each other and to B. thuringiensis entries in Genbank. B. thuringiensis with similar 16S rRNA gene sequences from these different zones were characterized with regard to maximum growth rate and temperature optima for growth to test if there was local adaptation in these functional traits. The result showed a narrow temperature range around 30°C for maximal growth rate, and there were no significant differences between agro-ecological zones. Of 110 Bacillus thuringiensis isolates analyzed for the presence of crystal protein genes,  7 tested positive for cry 4, cry 11, and cyt toxin genes. Sequencing of these genes in positive strains demonstrated 99–100 % homology to known mosquitocidal cry and cyt genes in Bacillus thuringiensis subsp. israelensis. The present study shows that this biotechnologically important species is wide spread in Ethiopian soils and that it does not demonstrate local adaptation to temperature regimes, at least not for basic functions such as growth-temperature response. Our finding also pointed the potential for exploiting this species in vector control programs.

Oxygen-isotopic composition and high-resolution secondary ion mass spectrometry imaging of Martian carbonate in Lafayette meteorite

Carbonate from SNC meteorites gives insight into a variety of processes on and/or beneath the surface of Mars. In Lafayette, carbonate occurs in unusually intimate association with hydrous phases when compared with other carbonate-bearing SNCs [1]. We have measured the ^(18)O/^(16)O ratio of carbonate in the alteration veins of Lafayette using the magnetic sector ion microprobe. In addition, we obtained isotope images of major- and minor-element cations in veinlets with the focused ion beam (FIB) quadrupole SIMS. The spot size of the FIB probe used in this study (~0.03 µm) provides an opportunity for high spatial resolution chemical imaging, which is ideal for examining features in the fine-grained alteration assemblage

Use of Clumped-Isotope Thermometry To Constrain the Crystallization Temperature of Diagenetic Calcite

We describe an approach to estimating the crystallization temperatures of diagenetic calcites using clumped-isotope thermometry, a paleothermometer based on the ^(13)C–^(18)O-bond enrichment in carbonates. Application of this thermometer to calcified gastropod shells and calcite cements in an early Eocene limestone from the Colorado Plateau reveals a record of calcite precipitation and replacement at temperatures varying from 14 to 123°C. The early Eocene host sediments were never deeply buried, but they experienced a significant thermal pulse associated with the emplacement of a late Miocene basalt flow. The combination of independent constraints on thermal history with clumped-isotope thermometry, petrographic (including cathodoluminescence) observations, and oxygen isotopic data provides an improved basis for estimation of the temperature and timing of diagenetic events and fluid sources. The petrography and calcite δ^(18)O values, taken alone, suggest that the aragonite-to-calcite transformation of gastropod shell material occurred simultaneously with early formation of cements and lithification of the matrix in the same sample. However, addition of clumped-isotope thermometry demonstrates that this phase transformation of shell material occurred at temperatures of 94–123°C in a highly rock-buffered microenvironment (i.e., with the isotopic composition of fluid buffered by coexisting carbonate), millions of years after lithification of the matrix and formation of initial low-temperature (14–19°C) calcite cements within shell body cavities. Clumped-isotope temperatures in excess of reasonable Earth-surface conditions recorded by later-formed cements demand that cement growth occurred in association with the lava emplacement. Our results illustrate the potential for clumped-isotope thermometry to constrain conditions of diagenesis and guide interpretations that would not be possible on the basis of conventional stable-isotopic and petrographic data alone, and demonstrate how petrographic characterization of clumped-isotope thermometry samples can benefit paleoclimate studies